Prior to the present invention, BPA polycarbonate, which hereinafter will mean polycarbonate obtained by preferably using 2,2-bis-(4-hydroxyphenyl)-propane or "Bisphenol-A" to produce the polycarbonate backbone, was utilized in a variety of applications requiring high impact resistance. On the other hand, polymethyl methacrylate, "PMMA", found wide use in glazing applications based on its high transparency, its comparatively high modulus of elasticity, and its high degree of scratch resistance and weathering resistance, particularly U.V. resistance. However, PMMA glazing suffers from low impact strength and from low heat distortion resistance. BPA polycarbonate also finds wide use in glazing applications based on its superb impact toughness, and its high heat resistance. However, BPA polycarbonate in comparison with PMMA has lower transparency, elastic modulus, scratch resistance, and weathering (UV) resistance. It would be desirable, therefore, to make transparent blends of BPA polycarbonate and PMMA to provide improved glazing materials and applications such as optical discs, combining many of the advantages of both BPA polycarbonate and PMMA. It is generally recognized, however, that PMMA and BPA polycarbonate are not miscible and blends would therefore be expected to be hazy or cloudy.
The present invention is based on my discovery that blends of BPA polycarbonate and polymethyl methacrylate, as defined hereinafter, can be cast as transparent films having a lower critical solution temperature (LCST) exceeding 120.degree. C., i.e. capable of remaining transparent unless heated to exceed such temperature. However, depending upon the nature of the polymethyl methacrylate, that is, whether it is free-radical polymerized or anionically-polymerized, and depending on the nature of the chain ends, e.g., alkyl mercapto groups, carboxyl groups, hydrogen atoms, etc., the ability to resist phase separation, that is, to become cloudy, can in some instances exceed temperatures as high as 300.degree. C. As a result, there is also provided by the present invention, melt processable blends of BPA polycarbonate and PMMA which can be converted to improved glazing materials and transparent optical discs.